U.S. patent application number 10/685703 was filed with the patent office on 2004-07-15 for chain tensioner.
Invention is credited to Hayakawa, Hisashi, Sato, Seiji.
Application Number | 20040138018 10/685703 |
Document ID | / |
Family ID | 32040836 |
Filed Date | 2004-07-15 |
United States Patent
Application |
20040138018 |
Kind Code |
A1 |
Hayakawa, Hisashi ; et
al. |
July 15, 2004 |
Chain tensioner
Abstract
A chain tensioner is provided, in which the design conditions of
a register ring are optimized in compliance with the required
functions so as to improve the durability, the operational
stability and the like of the chain tensioner. A register ring is
formed of a steel material having a tensile strength of 1000 to
3500 N/mm.sup.2. At the same time, an overlapping allowance of the
register ring with respect to engagement grooves of a plunger is
set within the range of 30 to 50% of a wire diameter of the
register ring. Furthermore, a bending stress generated in the
register ring when the register ring is made to slide between the
engagement grooves to increase its diameter is set within the range
of 500 to 1700 N/mm.sup.2.
Inventors: |
Hayakawa, Hisashi;
(Shizuoka-ken, JP) ; Sato, Seiji; (Shizuoka-ken,
JP) |
Correspondence
Address: |
ARENT FOX KINTNER PLOTKIN & KAHN
1050 CONNECTICUT AVENUE, N.W.
SUITE 400
WASHINGTON
DC
20036
US
|
Family ID: |
32040836 |
Appl. No.: |
10/685703 |
Filed: |
October 16, 2003 |
Current U.S.
Class: |
474/122 |
Current CPC
Class: |
F16H 2007/0806 20130101;
F16H 2007/0855 20130101; F16H 2007/0812 20130101; F16H 2007/0859
20130101; F16H 7/0836 20130101; F16H 2007/0878 20130101; F16H
2007/0853 20130101 |
Class at
Publication: |
474/122 |
International
Class: |
F16H 007/22 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 17, 2002 |
JP |
2002-303031 |
Claims
What is claimed is:
1. A chain tensioner comprising: a cylindrical housing with a
closed end; a plunger slidably fitted into the housing on an inner
circumference of the housing; a return spring for imparting outward
projection ability to the plunger; a plurality of engagement
grooves formed on an outer circumference of the plunger; a first
stopper formed on the inner circumference of the housing; and a
register ring capable of elastically increasing and reducing its
diameter, being engaged with the engagement grooves, any of the
engagement grooves being engaged with the first stopper through the
register ring to regulate backward movement of the plunger, wherein
the register ring is formed of a steel material having a tensile
strength of 1000 to 3500 N/mm.sup.2.
2. The chain tensioner according to claim 1, wherein an overlapping
allowance of the register ring with respect to the engagement
grooves of the plunger is set within a range of 30 to 50% of a wire
diameter of the register ring, and a maximum bending stress of the
register ring having an increased diameter, when it is positioned
between the engagement grooves, is within a range of 500 to 1700
N/mm.sup.2.
3. The chain tensioner according to claim 1 or 2, wherein the
register ring is formed of an oil-tempered wire. 33
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a chain tensioner for
keeping the tension of a chain constant, which is placed on a loose
side of the chain, in a chain transmission system for transmitting
the rotation of a crank shaft to a cam shaft, for example, in a
vehicle engine.
[0003] 2. Description of the Related Art
[0004] As the above-described chain tensioner, a chain tensioner
having the following structure is conventionally known. A spring
and a plunger are housed within a housing so that outward
projection ability is imparted to the plunger by an elastic force
of the spring. In this chain tensioner, the plunger, which is
elastically pressed by the spring, pushes the chain so as to bring
the chain into a tensed state. On the other hand, the pushing force
imparted to the plunger by the chain is buffered by an oil pressure
in an oil hydraulic damper chamber formed in the rear of the
plunger to keep a tensile force of the chain constant. As specific
structures, for example, those described in, for example, Japanese
Patent Laid-Open Publication Nos. 2001-146946 and 2001-355691 are
known.
[0005] In this type of chain tensioner, a register ring is provided
as a member for regulating the backward movement of the plunger
(return regulation). The register ring is engaged with a first
stopper formed on the inner circumferential surface of the housing
while being fitted into any of a plurality of engagement grooves
formed on the outer circumferential surface of the plunger. As
described above, the register ring plays an important role in
regulation of the backward movement of the plunger so as to prevent
the chain from being excessively loosened and the like.
[0006] As described above, the register ring is an important
component in view of realization of the functions of the chain
tensioner. Therefore, the design conditions of the register ring
such as a shape and a material should be deliberately determined in
consideration of the functions of the chain tensioner.
SUMMARY OF THE INVENTION
[0007] In view of the above-described requirements, the present
invention has an object of optimizing the design conditions of a
register ring in compliance with the required functions so as to
improve the durability, the operational stability, and the like of
a chain tensioner.
[0008] In order to achieve the above object, a chain tensioner
according to the present invention includes: a cylindrical housing
with a closed end; a plunger slidably fitted into the housing on
its inner circumference; a return spring for imparting outward
projection ability to the plunger; a plurality of engagement
grooves formed on an outer circumference of the plunger; a first
stopper formed on the inner circumference of the housing; and a
register ring capable of elastically increasing and reducing its
diameter, being engaged with the engagement grooves, any of the
engagement grooves being engaged with the first stopper through the
register ring to regulate backward movement of the plunger, wherein
the register ring is formed of a steel material having a tensile
strength of 1000 to 3500 N/mm.sup.2.
[0009] If the register ring is formed of a steel wire having a
tensile strength of 1000 to 3500 N/mm.sup.2 as described above, the
durability of the register ring can be enhanced.
[0010] An overlapping allowance of the register ring with respect
to the engagement grooves of the plunger is set within the range of
30 to 50% of a wire diameter of the register ring. At the same
time, the maximum bending stress of the register ring having an
increased diameter, when it is positioned between the engagement
grooves, is set within the range of 500 to 1700 N/mm.sup.2. As a
result, it is ensured that the backward movement of the plunger can
be regulated at engine stop and the like.
[0011] Moreover, the plunger can be made to follow the movement of
a chain so as to smoothly project even during engine operation.
[0012] In this case, if the register ring is formed of an
oil-tempered wire, the heat resistance of the register ring can be
ensured.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] In the accompanying drawings:
[0014] FIG. 1(a) is a plan view showing a chain tensioner according
to the present invention, and FIG. 1(b) is a side view thereof;
[0015] FIG. 2 is a sectional view taken along the line A-A in FIG.
1(a);
[0016] FIG. 3 is an enlarged plan view of the chain tensioner;
[0017] FIG. 4(a) is a plan view of a register ring, FIG. 4(b) is a
front view thereof, and FIG. 4(c) is a side view thereof;
[0018] FIG. 5 is a plan view of a housing in the step of inserting
the register ring;
[0019] FIG. 6 is a sectional view showing an operating state of the
chain tensioner;
[0020] FIG. 7 is a sectional view showing the chain tensioner at
the time of return movement regulation;
[0021] FIG. 8 is a sectional view showing the chain tensioner at
the time of disassembly regulation;
[0022] FIG. 9 is a diagram showing an idealized register ring;
[0023] FIG. 10 is a table showing the results of repeated strength
tests of the register ring; and
[0024] FIG. 11 is a sectional view for illustrating an overlapping
allowance of the register ring with respect to engagement
grooves.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] Hereinafter, embodiments of the present invention will be
described with reference to FIGS. 1(a) to 11.
[0026] As shown in FIGS. 1(a), 1(b) and 2, a chain tensioner
according to the present invention is assembled with the following
components serving as main components. The chain tensioner
includes: a housing 1; a plunger 3, a return spring 5 and a check
valve 6 accommodated in the housing 1 on its inner circumference;
and a register ring 7 fitted to the plunger 3 on its outer
circumference. In the following description, a direction in which
the plunger 3 projects with respect to the housing 1 is denoted as
a forward direction (the right side in FIGS. 1(a), 2, 3 and 6 to
8), whereas the opposite direction is denoted as a backward
direction (the left side in FIGS. 1(a), 2, 3 and 6 to 8).
[0027] The housing 1 has a cylindrical shape with a closed end,
including a circular hole shaped cylinder portion 11 for housing
the plunger 3 therein. Attachment portions 12 for attachment to an
engine block are formed on both sides of the housing 1 sandwiching
the cylinder portion 11 (see FIG. 1(a)). On a bottom 13 of the
housing 1, an oil feeding path 15 for guiding a working oil serving
as a working fluid from a tank 14 to the cylinder portion 11 is
formed. The housing 1 can be formed by, for example, turning a cast
made of cast iron (FC250 (according to JIS) or the like) or a light
alloy (aluminum alloy or the like) or the like.
[0028] At an open end of an inner circumferential surface 1a of the
housing, a notch 16 is formed in an axial direction at a position
in a circumferential direction. Through the notch 16, operational
portions 72 of the register ring 7 described below project toward
the outer circumferential side of the housing 1. An annular guide
groove 18 passing through the approximately middle portion of the
notch 16 in the axial direction is formed in the vicinity of the
open end of the inner circumferential surface 1a of the housing 1.
A first stopper 21 and a second stopper 22, each being engaged with
the register ring 7, are formed on both end faces of the opening of
the guide groove 18 in the axial direction. The first stopper 21
and the second stopper 22 can be integrally formed with the housing
1 as shown in FIG. 2. Alternatively, they can be formed as
independent members fitted into the housing 1 on its inner
circumference. In this embodiment, as an example, the first stopper
21 on the rear side is formed on a tapered face, whereas the second
stopper 22 on the front side is formed on a face in a radial
direction. However, the shapes of the first and second stoppers are
not particularly limited as long as it is ensured that the first
and second stoppers are engageable with the register ring 7.
[0029] A width of the guide groove 18 in the axial direction is
larger than a wire diameter of a ring portion 71 of the register
ring 7. Therefore, the ring portion 71 of the register ring 7 is
movable in the guide groove 18 in forward and backward
directions.
[0030] The plunger 3 is formed in a cylindrical shape with a closed
end so as to have a cylindrical hollow portion 31 on its rear side.
A return spring 5 in a compressed state is placed inside the inner
circumference of the hollow portion 31. One end of the return
spring 5 is supported by the bottom of the inner circumferential
surface of the plunger 3, whereas the other end of the return
spring 5 is supported by an upper end face of the check valve 6
provided on the bottom of the housing 1. As a result, an elastic
force in a forward direction always acts on the plunger 3 so that
the projection ability in the outward direction from the housing 1
is imparted to the plunger 3. A space between the bottom 13 of the
housing 1 and the plunger 3 (including the internal space of the
hollow portion 31), in other words, the cylinder portion 11
situated in the rear of the plunger 3 and the internal space of the
hollow portion 31 form an oil hydraulic damper chamber 9. The oil
hydraulic damper chamber 9 is filled with the working oil fed
through the oil feeding path 15.
[0031] On the outer circumferential surface of the hollow portion
31 of the plunger 3, a plurality of annular engagement grooves 33a
to 33d are formed at equal intervals in the axial direction. In
this embodiment, as an example, the four engagement grooves 33a to
33d are provided. In the following description, these engagement
grooves are denoted as the first engagement groove 33a to the
fourth engagement groove 33d from the front side.
[0032] As shown in an enlarged manner in FIG. 3, for each of the
engagement grooves 33a to 33d, wall surfaces 331 and 332 on both
sides in the axial direction, between which the deepest portion is
placed, are both formed in a tapered manner. However, the wall
surface 331 (lock surface) on the front side has a larger tilt
angle than that of the wall face 332 (tapered surface) on the rear
side. The lock surface 331 and the tapered surface 332 are smoothly
continued through a curved surface.
[0033] The tapered surface 332 of each of the engagement grooves
33a to 33d serves as a sliding surface on which the register ring 7
slides. A taper angle .theta. of the tapered surface 332(angle with
respect to the center of the axis of the plunger 3: see FIG. 3) is
too large, a sliding resistance is increased by sliding movement of
the register ring 7 to inhibit the smooth forward and backward
movement (in particular, the forward movement) of the plunger 3. On
the other hand, if the taper angle .theta. is too small, the
lengths of the engagement grooves 33a to 33d in the axial direction
become long. As a result, a return stroke of the plunger 3 at
engine stop becomes large to cause abnormal sounds at engine
restart. In view of the above inconveniences, the taper angle of
the tapered surface 332 is set within the range of 8.degree. to
20.degree., preferably, within the range of 10.degree. to
15.degree.. Similarly, in order to reduce a sliding resistance of
the plunger 3 and to obtain a stable sliding surface with a small
variation in friction coefficient, the engagement grooves 33a to
33d (in particular, their tapered surfaces 332) are finished to
have a surface roughness R.sub.max (JISB0601) of 6.3 .mu.m or less,
more preferably, 3.2 .mu.m or less.
[0034] In the rear of each of the engagement grooves 33a to 33d, a
cylindrical surface 34 is formed so as to be adjacent to each
tapered surface 332.
[0035] As shown in FIG. 2, among the engagement grooves 33a to 33d,
in the rear of the fourth engagement groove 33d positioned in the
last row, an annular safety groove 35 is formed. A wall surface of
the safety groove 35 on the rear side serves as a safety wall 351
engageable with the register ring 7. The register ring 7 being
engaged with the safety wall 351 is subsequently engaged with the
second stopper 22 on the inner circumferential surface 1a of the
housing 1, thereby restraining the plunger 3 from being pushed out
from the cylinder portion 11 (disassembly regulation).
[0036] An annular set wall 36 is formed in front of the first
engagement groove 33a positioned in the first row among the
engagement grooves 33a to 33d. The set wall 36 can be formed, for
example, as shown in FIG. 3, with a front surface of an annular
projecting portion 37 in a radial direction, the annular projecting
portion 37 being formed in front of the first engagement groove
33a. The register ring 7 being engaged with the set wall 36 is
engaged with the second stopper 22 of the inner circumferential
surface 1a of the housing 1, thereby maintaining the chain
tensioner in its initial set state (state shown in FIG. 2).
[0037] The plunger 3 can be formed by forging a steel material such
as carbon steel for machine construction, chromium steel,
chromium-molybdenum steel and manganese steel for machine
construction (preferably, containing carbon at 0.25% or less in
view of the processability, the hardenability, the cost and the
like). After forging, each of the engagement grooves 33a to 33d on
the outer circumferential surface of the plunger 3 is formed by
plastic processing (for example, component rolling) or mechanical
processing to have the above-described surface roughness (it is
apparent that the other grooves such as the safety groove 35 can be
processed by a similar processing method). After the plunger
material, on which the grooves have been formed, is subjected to a
thermal treatment such as carburizing and quenching, the outer
circumferential surface of the hollow portion 31 of the plunger 3
and the cylindrical surface 34 are finished by centerless grinding.
As a result, a fitting surface onto the inner circumferential
surface 1a of the housing 1, which affects the amount of leak of
the working oil or a sliding resistance of the plunger 3, is
finished with predetermined precision.
[0038] If air enters the oil hydraulic damper chamber 9, the
buffering functions in the oil hydraulic damper chamber 9 are
adversely affected. Therefore, the entrained air is required to be
exhausted to the exterior of the oil hydraulic damper chamber 9 by
some method. From this point of view, an air vent hole 38 is formed
in a bottom 32 of the plunger 3 in the illustrated example. The air
vent hole 38 in the illustrated example is formed in a spiral
manner by forming a female screw hole in the bottom 32 in the axial
direction and pushing an axial member 39 into the screw hole. The
air vent hole can alternatively be formed on the housing 1 side,
depending on the angle at which the chain tensioner is
attached.
[0039] The check valve 6 is provided adjacent to the bottom 13 of
the housing 1. The check valve 6 is constituted by, for example, a
valve seat 61, a valve body 63 (for example, a steel ball) for
opening and closing a valve hole 62 formed through the valve seat
61, and a retainer 64 for limiting the amount of opening/closing of
the valve body 63. When the oil feeding path 15 has a higher
pressure than that of the oil hydraulic damper chamber 9, the check
valve 6 opens the valve hole 62 so that the working oil flows from
the oil feeding path 15 into the oil hydraulic damper chamber 9. On
the other hand, when the oil hydraulic damper chamber 9 has a
higher pressure than that of the oil feeding path 15, the check
valve 6 closes the valve hole 62 so that the working oil in the oil
hydraulic damper chamber 9 is prevented from reversely flowing into
the oil feeding path 15.
[0040] The register ring 7 includes, as shown in FIGS. 4(a) to
4(c), an annular ring portion 71, and the operational portions 72
for increasing the diameter of the ring portion 71. The register
ring 7 is formed by, for example, crossing both ends of a rolled
wire material. The operational portions 72, which are situated on
the outer diameter side of the crossing portion, are brought close
to each other in the circumferential direction, thereby elastically
increasing the diameter of the ring portion 71. In this case, both
ends of the operational portions 72 are bent in the axial direction
to form tab portions. These tab portions facilitate the operation
of increasing the diameter of the ring portion 71. A step portion
73 in the axial direction is provided for the ring portion 71 in
the vicinity of the crossing portion of the wire material. In this
manner, the most part of the ring portion 71 is situated on a plane
perpendicularly crossing the axial direction. The above-described
register ring 7 corresponds to a so-called formed wire spring, that
is, a wire material bent in an appropriate shape to perform a
spring action. This type of spring has similar shape and functions
as those of the hose clip according to the Japanese Automobile
Standards JASO F204.
[0041] A material of the register ring 7 is appropriately selected
for use from the group consisting of spring steel, a piano wire, a
hard steel wire, an oil-tempered wire, a stainless steel wire and
the like. A material is selected in consideration of a limit of
elasticity, an elastic modulus, a fatigue strength, a
hardenability, a heat resistance, a corrosion resistance, a thermal
expansion and the like. In this embodiment, an oil-tempered wire,
in particular, a silicon-chromium steel oil-tempered wire for valve
spring, SWOSC-V, according to JIS G3566 (in this embodiment, one
with a circular cross section and a wire diameter of 0.8 mm) is
used so as to be compatible with an increase in temperature of the
operating environment (at 120.degree. C. or higher). The
oil-tempered wire is cold-worked to form the register ring 7 in
this embodiment. The oil-tempered wire is formed in the following
manner. After a wire material such as carbon steel or low-alloy
steel is cold-worked and is drawn into a wire so as to obtain good
dimensional accuracy and surface conditions, the material in a wire
form is quenched and tempered in a successive manner so as to be
provided with appropriate mechanical properties. A spring formed by
using this wire has approximately similar structure and
characteristics to those of a hot formed spring. This spring has a
higher ratio of the limit of elasticity and the yield strength to
the tensile strength as compared with steel wires formed by cold
working and drawing, and is therefore advantageous in that a high
heat resistance can be expected. If the heat resistance is not
considered as a quite important factor, a piano wire such as SWP-A,
SWP-B or SWP-V according to JIS, which is advantageous in terms of
cost and processability, can also be used. A wire diameter P of the
register ring 7 (see FIG. 11) is desirably within the range of 0.8
to 1.2 mm.
[0042] The register ring 7 is formed so that, in its natural state
(in a state where the diameter of the register ring 7 is not
increased), an inner diameter of the ring portion 71 is smaller
than an inner diameter of the open end of the inner circumferential
surface 1a of the housing 1 (in the illustrated example, the inner
diameter of the second stopper 22) and an outer diameter of the
ring portion 71 is larger than the inner diameter of the open end.
Since the notch 16 is formed for the housing 1, the register ring 7
can be easily attached to the housing 1 by inclining the register
ring 7 even if the register ring 7 has a larger outer diameter than
the inner diameter of the housing 1 on its inner circumference as
described above (see FIG. 5).
[0043] After the check valve 6 is attached to the cylinder portion
11, the register ring 7 is attached and the return spring 5 is
inserted. Then, the plunger 3 is inserted into the cylinder portion
11 while the operational portions 72 projecting outside the housing
1 are being picked (either manually or by a tool) to increase the
diameter of the ring portion 71. The plunger 3 is pushed into the
cylinder portion 11 against the elastic force of the return spring
5. When the set wall 36 reaches the position in the rear of the
ring portion 71 of the register ring 7, the operational portions 72
are released to elastically reduce the diameter of the ring portion
71 of the register ring 7. At the same time, the pushing force
applied on the plunger 3 is cancelled so that the set wall 36 is
engaged with the ring portion 71 of the register ring 7.
Furthermore, the ring portion 71 is engaged with the second stopper
22 on the inner circumference of the housing 1 so as to realize the
initial set state shown in FIG. 2. In this initial set state, the
set wall 36, the register ring 7, and the second stopper 22 are
mutually engaged so that it is ensured that the plunger 3 is
restrained from being pushed out by the elastic force of the return
spring 5. Therefore, the safety in transport and the like is
improved.
[0044] After attachment of the chain tensioner in this initial set
state to the engine block, the operational portions 72 of the
register ring 7 are pushed together to increase the diameter of the
ring portion 71 of the register ring 7, thereby canceling the
engaged state between the set wall 36 and the register ring 7. As a
result, the plunger 3 moves forward owing to the elastic force of
the return spring 5 to push the chain through a chain guide (not
shown). In this manner, the chain is brought into a tensed
state.
[0045] At this moment, as shown in FIG. 6, the ring portion 71 of
the register ring 7 is fitted into any of the engagement grooves
33a to 33d (in FIG. 6, the second engagement groove 33b) or is
positioned on the cylindrical surface 34 positioned in the rear of
each of the engagement grooves 33a to 33d. Thereafter, during
engine operation, as a result of the tension of the chain, a
backward pushing force acts on the plunger 3. When the pushing
force exceeds the resultant force of the elastic force of the
return spring 5 and the pressure of the oil fed in the oil
hydraulic damper chamber 9, the plunger 3 and the register ring 7
move backward to reach the position where the resultant force and
the pushing force become equal to each other. This backward
movement proceeds slowly by the buffering functions of the working
oil filling the oil hydraulic damper chamber 9. During the backward
movement of the plunger 3, the register ring 7 reduces its diameter
while first sliding on the tapered surface 332 serving as a sliding
surface from the state shown in FIG. 6. When the register ring 7 is
engaged with the lock surface 331 of the engagement groove 33b, the
register ring 7 moves backward cooperatively with the plunger 3
while being engaged with the lock surface 331. Along with the
backward movement of the plunger 3, an excessive working oil in the
oil hydraulic damper chamber 9 leaks outside the housing 1 through
an extremely small gap between the inner circumferential surface 1a
of the housing 1 and the outer circumferential surface of the
plunger 3.
[0046] On the other hand, once the chain is loosened, the plunger 3
moves forward by the pushing force corresponding to the resulting
force of the return spring 5 and the pressure of the fed oil. Along
with the forward movement of the plunger 3, the register ring 7
moves forward cooperatively with the plunger 3. After the ring
portion 71 is abutted against the second stopper 22, the register
ring 7 increases its diameter while sliding on the tapered surface
332. In the case where the chain is loosened with elapse of time
and the plunger 3 further moves forward, the ring portion 71 of the
register ring 7 passes over the cylindrical surface 34 so as to be
fitted into the engagement groove (in FIG. 6, the third engagement
groove 33c) in the rear of the cylindrical surface 34. From then
on, a similar operation to that in the case where the ring portion
7 is fitted into the second engagement groove 33bis performed.
[0047] When the engine is stopped, the plunger 3 is sometimes
significantly pushed into the cylindrical portion 11, depending on
the relation with a position where a cam is stopped. For example,
when the engine is stopped while a change lever is shifted to
operate a forward gear on the uphill or the change lever is shifted
to operate a back gear on the downhill, the chain is sometimes
tensed. In this case, the plunger 3 is significantly pushed into
the cylindrical portion 11. Even in this case, since the outer
diameter of the ring portion 71 of the register ring 7 is larger
than the inner diameter of the first stopper 21 as shown in FIG. 7,
the register ring 7 (the ring portion 71) engaged with the lock
surface 331 of the engagement groove (for example, the second
engagement groove 33b) is subsequently engaged with the first
stopper 21. As a result, further backward movement of the plunger 3
is regulated (return movement regulation). In this case, the chain
is loosened only by the amount corresponding to the amount of
backward movement of the plunger 3. Therefore, even if the engine
is restarted, the chain is not significantly loosened. Accordingly,
the problems such as the chain coming off a sprocket, the chain
skipping or the generation of abnormal sounds can be avoided.
[0048] When the chain is detached for maintenance around the
engine, the elastic force of the return spring 5 is likely to push
out the plunger 3. Even in such a case, however, the ring portion
71 of the register ring 7 is fitted into the safety groove 35 as
shown in FIG. 8 so that the ring portion 71 engaged with the safety
wall 351 is subsequently engaged with the second stopper 22 to
restrict the plunger 3 from being pushed out therefrom (disassembly
regulation). In this manner, it is ensured that the components such
as the plunger 3 and the return spring 5 can be prevented from
coming off the housing 1. Even in the case where the plunger 3 is
to be removed from the housing 1, the operational portions 72 of
the register ring 7 are picked together to increase the diameter of
the ring portion 71 so as to cancel the engagement between the ring
portion 71 and the safety wall 351. As a result, the
above-described removal of the plunger 3 can be easily
realized.
[0049] As described above, the register ring 7 follows the
forward/backward movement of the plunger 3 to move
forward/backward. However, when the operational portions 72 of the
backwardly moving register ring 7 collide against a wall surface
16a on the bottom of the notch 16 (see FIG. 3), there is a
possibility that the register ring 7 might be deformed by this
shock. Therefore, a measure to prevent the operational portions 72
of the backwardly moving register ring 7 from contacting the wall
surface 16a is desired. Such a measure can be realized by, for
example, setting a length D of the notch 16 in the axial direction
to be larger than a distance X (a distance from the open end of the
housing 1 to the rear end of the register ring 7 in the notch 16 at
the time when the lock surface 331 of the engagement groove is
engaged with the first stopper 21 through the register ring 7)
(D>X), as shown in FIG. 3.
[0050] As described above, according to the chain tensioner of the
present invention, the initial set state, the return movement
regulation and the disassembly regulation can be realized only by
using the register ring 7. Accordingly, as compared with the case
where these functions are realized with a plurality of ring members
or clips, the number of components and the fabrication cost can be
significantly reduced. Furthermore, the structure of the grooves on
the plunger 3 is simplified. In addition, each of the grooves is
formed on the outer circumferential surface of the plunger 3 which
is easy to process. Therefore, the processing cost can be further
held down. Moreover, since the plunger 3 can be removed from the
housing 1 with a simple operation, maintenance can be easily
realized.
[0051] The register ring 7 is used under a high-temperature
environment for a long period of time. Moreover, it should be
ensured that its diameter is reduced and increased as required.
Therefore, the design of the register ring 7 is required to be
deliberately examined so that its operability is stably ensured
even under such a harsh environment for a long period of time and
the requirements of cost are satisfied as well.
[0052] As a result of examinations of the inventors of the present
invention, the following characteristics are found to be the most
important as the characteristics of the register ring 7:
[0053] I) It is ensured that the amount of backward movement of the
plunger 3 is kept to a predetermined amount or less at engine
stop;
[0054] II) The projection ability of the plunger is not affected by
a sliding resistance generated when the register ring has its
increased diameter; and
[0055] III) A dimensional change, which may damage the register
ring or cause its functional problems, is not caused by the fatigue
due to the movement of the register ring 7 for increasing/reducing
its diameter during engine operation.
[0056] In order to satisfy the above-described characteristic
requirements, the inventors of the present invention have continued
conducting the examination, focusing attention on an overlapping
allowance of the register ring 7 with respect to the engagement
grooves 33a to 33d, a bending stress generated at the time when the
register ring 7 has an increased diameter, and a tensile strength
of the material of the register ring 7. As a result, the inventors
of the present invention have found the following preferable ranges
thereof.
[0057] First, the backward movement regulation of the plunger (the
above-mentioned characteristic I) can be realized in the following
manner. An overlapping allowance of the register ring 7 with
respect to the engagement grooves 33a to 33d of the plunger 3 is
set at 30% or more of a wire diameter of the register ring 7. At
the same time, a bending stress applied to the register ring 7 when
the register ring 7 has the maximum diameter is set at 500
N/mm.sup.2 or more.
[0058] The term "overlapping allowance" herein indicates the
maximum width H of a cross-sectional region of the register ring 7,
which is delimited by the profile of the outer circumferential
surface of the plunger on the forward side of the engagement
grooves 33a to 33d, as shown in FIG. 11. In this embodiment, for
the first engagement groove 33a, the outer circumferential surface
of the annular projecting portion 37 corresponds to the "outer
circumferential surface of the plunger on the forward side." For
the second to the fourth engagement grooves 33b to 33d, the
cylindrical surface 34 corresponds thereto. In the present
invention, a ratio H/P of the maximum width H to the wire diameter
P of the register ring 7 (more specifically, the ring portion 71)
is set at 30 to 50%. The maximum width H is identical with a depth
of the engagement groove in the case where the register ring 7 is
fitted into any of the engagement grooves 33a to 33d to reach its
deepest portion.
[0059] If the overlapping allowance is smaller than 30% of the wire
diameter D, the register ring 7 is likely to pass over a forward
side of the outer circumferential surface of each of the engagement
grooves 33a to 33d when a backward force is applied to the plunger
3. As a result, there is a possibility that the backward movement
may be insufficiently regulated. On the other hand, the overlapping
allowance exceeds 50% of the wire diameter D, it becomes difficult
to cancel the initial set state, resulting in complicated engine
assembly. Accordingly, the ratio H/P is required to be set at 50%
or less of the wire diameter D.
[0060] Moreover, as described above, the register ring 7 increases
its diameter while traveling between the engagement grooves, and
has the maximum diameter when passing over the outer
circumferential surface of the plunger 3 (in this embodiment, the
cylindrical surface 34). If the maximum bending stress generated in
the register ring 7 when the register ring 7 has the maximum
diameter is smaller than 500 N/mm.sup.2, the backward movement
regulating force generated in the register ring 7 becomes
insufficient in consideration of dimensional tolerances of the
register ring 7, the engagement grooves 33a to 33d and the like. As
a result, reliable backward movement regulation is impeded.
[0061] Next, the projection ability of the plunger 3 (the
above-mentioned characteristic II) can be realized by setting the
maximum bending stress generated in the register ring 7 when the
register ring 7 has the maximum diameter at 1700 N/mm.sup.2 or
less. With a bending stress exceeding 1700 N/mm.sup.2 or less, a
sliding resistance generated when the plunger 3 outwardly projects
is remarkably increased to degrade the followability of the plunger
to variation in chain tension.
[0062] In view of the above-described facts, it is desirable that
the maximum bending stress of the register ring 7 is set within the
range of 500 to 1700 N/mm.sup.2.
[0063] Next, for the fatigue resistance of the register ring 7 (the
above-described characteristic III), it is desirable that a
material of the register ring 7 has a tensile strength of 1000
N/mm.sup.2 or higher. In the case where the tensile strength is
smaller than 1000 N/mm.sup.2, a sufficient fatigue resistance of
the register ring 7 cannot be obtained to lower its durability.
Moreover, the strength of the register ring 7 becomes unstable when
the plunger 3 is significantly pushed into the cylinder portion 11
due to a delay in oil feeding at engine start to apply an impact
load on the register ring 7. The upper limit of the tensile
strength of the material of the register ring 7 is preferably set
at 3400 N/mm.sup.2 or less, desirably, 2400 N/mm2 or less in view
of the cost, the availability and the like.
[0064] The above-mentioned silicon-chromium steel oil-tempered wire
for valve spring (SWOSC-V) satisfies all the above-described
conditions, i.e., the bending stress (500 to 1700 N/mm.sup.2) and
the tensile strength (1000 N/mm.sup.2 or higher).
[0065] For the design of the register ring 7, a material of the
register ring 7 is required to be selected from the group of
materials having the maximum bending stress (the bending stress at
the time when the register ring 7 has the maximum diameter) of 70%
or less of the tensile strength of the material. Hereinafter, it is
confirmed whether this condition is satisfied or not in the case
where the oil-tempered wire for valve spring (SWOSC-V) is used as a
material of the register ring 7. The following description assumes
the case where the register ring 7 having an inner diameter .phi.
of 13 is formed of a wire material having a wire diameter .phi. of
1.
[0066] First, the register ring 7 is idealized as a C-shaped curved
beam shown in FIG. 9. When a force P is applied onto both ends of
the beam in a direction perpendicular to a line connecting the end
and the center thereof, an internal energy U accumulated in the
beam is expressed by the following formula. 1 U = 0 s M 2 2 EI z s
( 1 )
[0067] According to the Castigliano's principle, a deflection
.delta. is calculated by the following formula. 2 = U P ( 2 )
[0068] A bending moment M in a cross section m is calculated
by:
M=Pr(1+cos .phi.) (3)
[0069] By substituting the formula (3) for the formula (1), 3 U = 1
2 EI z 0 P 2 r 3 ( 1 + cos ) 2 ( 4 )
[0070] is obtained. According to the formulae (2) and (4), 4 = Pr 3
EI z 0 ( 1 + 2 cos + cos 2 ) = Pr 3 EI z [ + 2 sin + 1 4 sin 2 + 2
] 0 = Pr 3 EI z ( + 2 ) = ( 3 Pr 3 2 EI z ) ( 5 )
[0071] Herein, substituting the values:
E=206 (GPa)=2.06.times.10.sup.5 (N/mm.sup.2)
r=7 (mm)
I.sub.Z=.pi.d.sup.4/64 (d=1(mm)), for the above formula (5),
.delta.=0.16 P (6)
[0072] is deduced. It is experimentally elucidated that the ring
can be opened with .delta.=1.6 (mm). Therefore, by substituting
this value for the formula (6), an opening force P is obtained as:
P=10(N). Accordingly, the register ring 7 can be opened with a
moderate opening force P.
[0073] The maximum bending stress is generated at a point on the
diameter opposite to the ends of the wire material. A value of the
maximum bending stress is expressed by:
.sigma..sub.max=Mmax/Z (7)
[0074] (where Z=.pi.d.sup.3/32: moment of inertia of the cross
section). According to the formula (2), M.sub.max is calculated
with .phi.=0. Therefore,
Mmax=2Pr (8)
[0075] is obtained.
[0076] By substituting the formula (8) for the formula (7),
.sigma..sub.max is obtained as:
.sigma..sub.max=64 Pr/.pi.d.sup.3
[0077] By substituting:
P=10 (N)
r=7 (mm)
d=1 (mm)
[0078] for the above formula,
.sigma..sub.max=1426 (N/mm.sup.2)
[0079] is obtained. This obtained value corresponds to 70% of the
tensile strength, i.e., about 2100 (N/mm.sup.2), of the
oil-tempered wire for valve spring (SWOSC-V) having a wire diameter
.phi. of 1.00 (mm). Consequently, it is confirmed that the maximum
bending stress of an actual register ring corresponds to 70% or
less of its tensile strength.
[0080] Subsequently, the durability of the above-described register
ring is actually confirmed through a repeated load test. The test
is conducted by:
[0081] (1) measuring three points on the inner diameter of the
register ring with a profile projector to calculate a diameter;
[0082] (2) applying a repeated load to the register ring for 100
times until the register ring reaches its maximum deformation;
and
[0083] (3) repeating the procedure (1) to compare the diameters
before and after the test.
[0084] The results of measurement are shown in FIG. 10.
[0085] As can be seen in FIG. 10, a significant difference equal to
or larger than a measurement error is not observed between before
and after the repeated load test. In any case, a difference falls
within the range of 0.2% of the initial inner diameter. Based on
this result, it is confirmed that a permanent strain caused by the
repeated use does not remain in the register ring 7 and therefore
the register ring 7 has sufficient strength. The operation of the
register ring 7 for increasing its diameter is performed on
assembly or when the register ring 7 is opened at the initial set,
and is therefore performed only several times in a normal use.
[0086] Since a sufficient amount of oil is not fed to the oil
hydraulic damper chamber 9 at engine start in the chain tensioner
according to the present invention, it is not certain if a
lubricating state is realized at the register ring 7, on the lock
surface 331 of the plunger 3 and the abutting portion of the first
stopper 21 in a locked state (a state shown in FIG. 7). Therefore,
a load amplitude is applied to the plunger 3 in the locked state to
confirm the durability of the lock surface 331.
[0087] First, the chain tensioner itself is tested under the
following conditions; load amplitude: 100 N to/from 1000 N;
frequency shift: 120 Hz; lubrication state: oil application;
temperature for evaluation: room temperature; and the number of
application of the load amplitude: 1.times.10.sup.7. As a result,
the amount of wear is 10 .mu.m or less on either the lock surface
331 or the first stopper 21. Therefore, no particular problem is
generated in terms of the durability.
[0088] Next, the chain tensioner is attached to an actual engine,
and a similar test is conducted with no oil supply (where the
number of engine revolutions: 2000 r/min; and endurance time: 200
hours). Even in this case, the amount of wear is similarly 10 .mu.m
or less, and no particular problem is generated.
[0089] According to the present invention, since the register ring
is formed of a steel material having a tensile strength of 1000 to
3500 N/mm.sup.2, a fatigue life of the register ring can be
prolonged to provide a chain tensioner having high durability.
[0090] Furthermore, the overlapping allowance of the register ring
with respect to the engagement grooves of the register ring is set
at 30 to 50% of a wire diameter of the register ring. At the same
time, the maximum bending stress of the register ring having an
increased diameter between the engagement grooves is set at 500 to
1700 N/mm.sup.2. Therefore, the backward movement regulation of the
plunger at engine stop can be ensured. Moreover, the followability
of the plunger to variation in chain tension can be enhanced.
Accordingly, the chain tensioner having good operational stability
can be provided.
* * * * *